Complexes of molybednum in the higher oxidation states (IV,V, and VI) with sulfur-containing ligands may serve as structural models for the substrate-binding site in the nitrogenase enzyme system. By investigating correlations between molecular geometry and electronic structure for a variety of molybdenum-sulfur complexes, some insight into the structural possibilities for the enzymatic molybdenum-binding site may be gained, and the relationship of structural and functional properties in these systems may be elucidated. As a logical extension, the chemistry of the synthetic analogues with nitrogen-donor ligands will be studied with a view to the formation of complexes containing molybdenumnitrogen multiple bonds. The suggestions of imido-, hydrazido-, or diimido- formation as an intermediate stage in the production of ammonia from dinitrogen make resulting structural and electrochemical correlations of great interest.